A concise guide for safe and practical use of polyacrylamide (PAM) for
irrigation-induced erosion control and infiltration enhancement.
USDA-ARS Northwest Irrigation and Soils Research Laboratory Station Note
Prepared by R.E. Sojka, R.D. Lentz, D.L. Bjorneberg, and J.K. Aase, Northwest
Irrigation and Soils Research Lab, USDA-Agricultural Research Service,
3793N-3600E, Kimberly, ID 83341
Commercial use of polyacrylamide (PAM) in irrigation water began in 1995
and has been enormously successful and environmentally beneficial.
Over 600,000 acres were PAM-treated in the USA in 1997. The overseas
market is much larger. The USDA Natural Resources Conservation Service
has recognized the Kimberly ARS development of this technology as possibly
the most successful soil conservation practice ever developed for furrow
irrigation. New uses for the PAM soil conservation technology are
being developed at a rapid pace. This pamphlet gives practical considerations
for PAM-use in furrow and sprinkler irrigation, drawing on research conducted
by the Kimberly ARS team since 1991, and from other published sources.
PAM Material Considerations:
Purchase only polyacrylamide (PAM) officially labeled for irrigation erosion
control by your state (37 states currently have agricultural soil fertilizer and amendment laws
governing product label/registration). Purchasing from known reputable
agri-chemical suppliers may avoid acquiring ineffective or dangerous formulations
inappropriate for this use. In the USA this restricts use to PAMs with
the following properties:
- Anionic PAMs (negatively charged)-NOT CATIONIC (cationic PAMs can harm
the environment). Negative charge density may vary from 2 to over 30%,
but 18% is typical.
- Less than 0.05% free acrylamide monomer (AMD) by weight (<0.025% in
- Moderate to high molecular weights (typically 12 to 15 Mg/mole). Some
PAMs used mainly for infiltration enhancement have lower molecular weights.
- Designated as "water soluble", "linear", or "non-crosslinked" PAMs (NOT:
gel-forming, super-water absorbent, crosslinked, or non-linear. These are
not soluble and/or not suited for erosion control).
Purchase PAMs with reasonably high chemical analysis regardless of "type
of formulation". PAMs are available in a number of formulation types. The two most common
forms are as dry granular beads/powders or as concentrated inverse emulsions.
The dry forms of PAM should be expected to be 80% or greater active ingredient
(ai) by weight. Inverse emulsions are usually either 30 or 50% ai. In rare
instances PAM can be purchased as straight aqueous solutions, however viscosity
limits these to 3% ai. PAM is also available as large blocks or cubes. Remember that regardless of form or cost, the amount of PAM purchased
is determined by how much active ingredient is in the product. Each PAM form provides ease of application for a specific need, but be
sure how much you are paying for PAM active ingredient and how much you
are paying for convenience of application. A typical price range for PAM
at this writing is $3 to $6 per pound of PAM active ingredient.
Shelf life and storage needs should be considered at the time of purchase. Buy only the PAM needed for a given growing season, as full-potency shelf
life for most forms is only about one year. Some loss of effectiveness
may be noted when using PAM that is more than a year old. All PAM forms
should be stored in cool dry places away from direct sources of sunlight
to avoid PAM breakdown and loss of potency. Avoid freezing of liquid forms.
Emulsified concentrates may need some mixing before injection or dilution
if stored for prolonged periods because PAM and carrier may separate (like
oil-base paint). If spills occur, avoid traffic in the spill area, especially
if wet, since high concentration PAM solutions are extremely slippery and
can cause accidents. Clean thoroughly with sand, sawdust, or the like before
attempting to wash down the spill with water.
Note the following use considerations for the various forms of PAM:
Dry PAM forms are easy to store, transport and meter into head ditches
but require vigorous agitation to dissolve. Numerous inexpensive metered
applicators are available. Dry applicators should be placed on the head
ditch immediately above a source of turbulence, and if possible, 100-300
ft before the first irrigated furrow. When applying PAM powder via a turbulent
fountain with a weed screen, be sure to apply the PAM
below the screen
(outflow side) to prevent clogging of screens; a small hole may need to
be cut in the screen to allow for this. Powder forms can be easily sprinkled
in dry patches at the furrow inflow point (typically 0.5 to 1 ounce per
furrow), but care should be taken to avoid over application. Spread the
patch along the first 3-5 feet of furrow to avoid burying or loss of PAM
by the furrow stream.
Aqueous PAM concentrates accelerate the dissolving of PAM in head ditches,
but are very high in viscosity, bulkier than dry forms or inverse emulsion
concentrates, have low ai and are now rarely available commercially. Protect
against freezing during winter storage.
Emulsified Concentrates (Inverse Emulsions) are flowable liquid concentrates
with the appearance and viscosity of cream. The terminology "inverse emulsion"
refers to the chemical encapsulation of PAM molecules by minute amounts
of mineral spirits, which in turn are covered with a surfactant layer.
This allows high concentration (typically 30-50% PAM ai) in liquid form
without the high viscosity of aqueous emulsions. When inverse emulsions
are dispersed in water, the surfactant strips away the mineral spirit encapsulating
layer, releasing the PAM. Emulsified concentrates can provide enhanced
dissolution when used in head ditches, but still require moderate mixing
at the point of addition to the water stream. Experience has shown that
when emulsified concentrates are stored for long periods, some mixing of
the concentrate is needed before use to prevent separation of the PAM from
the carrier. Emulsified concentrations are bulkier than dry forms, but
add convenience of dispensing and mixing. If PAM is to be used in sprinkler
irrigation then the emulsified concentrate form of PAM is required.
Blocks or Cubes of PAM are solid PAM forms. Blocks typically weigh 2 pounds.
Percent ai is 54.5%. Blocks are suspended in baskets in flowing ditches
at turbulent points and slowly dissolve to deliver low concentrations of
PAM. Blocks do not perform as well as other PAM forms for furrow irrigation
erosion control, but have been useful for dosing settling ponds to promote
flocculation and to accelerate water clarification, or to dose concentrated
runoff areas on fields that otherwise cause severe uncontrolled erosion.
Blocks contain 40% polyethelene glycol (PEG) by weight.
Regardless of form, consider safety needs at all times.
READ THE LABEL
Properly registered PAMs for use as soil amendments for irrigation induced
erosion control will have specific safety instructions for each product.
In general, this class of PAMs is relatively safe compared to fungicides,
herbicides and insecticides. However, common sense precautions should prevail.
Avoid prolonged contact with the skin. If using dry forms, avoid inhaling
dust and keep it out of eyes. Rinse exposed areas thoroughly to avoid skin
Be aware that, although all PAMs are polymers, NOT ALL POLYMERS ARE PAM.
The media's recent high interest in PAM and the many stories reporting
the effectiveness of PAM have often referred to PAM only as "the polymer."
This has encouraged some entrepreneurial exploitation of the word "polymer"
in the agri-chemical community. The results achieved with the specific
class of PAMs described herein are not known to be achievable with other
affordable chemical polymers. Again, purchasing from known reputable agri-chemical
supply sources is the best way to avoid problems.
PAM Use Considerations:
Always add PAM slowly to turbulent water; NEVER ADD WATER TO PAM. If water is added to PAM, or if PAM is added to water so fast that wet
PAM grains or emulsion drops contact each other before completely dissolving,
a gel layer forms around the partially hydrated drops. This essentially
stops the remaining PAM from dissolving. Globs (sometimes called "fish
eyes" because of their appearance) or gel slabs form that do not dissolve.
These globs can clog pipes, dispensers etc. They can be washed away in
the water flow without providing any benefit in the field, resulting in
under-application because of incomplete dissolving of dispensed PAM. An
exception to this rule is use of the PAM patch application method, in which
0.5 to 1 ounce of PAM is sprinkled along the furrow-bottom just below the
water source prior to turning in the water. With the patch method, you
are intentionally forming a small gel slab at the inlet of the furrow.
The slow dissolving of the slab by the furrow stream doses the irrigation
PAM stabilizes existing soil structure but cannot improve soil structure. PAM-use is not a substitute for good soil management. If soils are compacted
or aggregate structure is degraded, PAM used in irrigation water cannot
rehabilitate the soil to an unimpaired condition. A minor exception to
this rule of thumb is that PAM promotes formation of a more permeable soil
surface than otherwise results during seal formation with untreated water.
When suspended sediments in the furrow stream flocculate and settle out,
they coat furrow bottoms with the precipitated solids. Seal formation can
occur as a result of deposition of particles initially detatched by erosion,
or even without erosion, if irrigation water is high in suspended solids
because of upstream contamination with sediment-laden return flows. When
PAM is used, seals still form, but they are more permeable (because of
floccule structure and aggregation of deposited sediment) than in the absence
The first drop of water to reach the furrow should already contain the
desired amount of dissolved PAM. PAM stabilizes soil to prevent erosion and surface sealing-which improves
infiltration. To stabilize the soil in optimal condition, PAM must be delivered
before the structure is destroyed by untreated flowing water. Adding PAM
to the furrow after untreated water has already begun to flow, usually
helps reduce erosion, but it also stabilizes the surface seal created by
the untreated water. As a result, PAM cannot improve infiltration as much
as it could have done if added immediately.
If using PAM in sprinkler irrigation, pressurize the pipe and be sure
water is being delivered before injecting PAM into the flow. This protocol assures that PAM does not build up in sprinkler lines before
water enters the pipes (which would violate the caution of not adding water
to PAM). The small amount of water sprinkled before beginning PAM injection
does not significantly affect soil properties before PAM stabilization
If irrigation water is high in sediment, addition of PAM to the flow can
cause settling of sediment in the head ditch or in gated pipe. If irrigating with water high in sediment content, the patch application
method may be the best approach to avoid siltation of ditches or pipes.
Construction of a small pond at the head ditch for PAM mixing can provide
a place for sediments to settle without blocking the main reaches of the
ditch. If using gated pipe, turn the gates a little more downward to favor
washing out sediments. Be sure that siphon tubes are not set so low in
the head ditch that they clog if sediment begins collecting. Increasing
siphon tube size will usually prevent tube clogging. High sediment loads
may require a slight increase of the PAM application rate to compensate
for PAM deactivated by flocculation of suspended sediment.
Do not over apply PAM. Research has confirmed that 10 ppm of PAM in advancing water (the NRCS
standard application method) provides erosion control in a wide range of
circumstances on nearly all soils. The NRCS standard should be used whenever
soil is disturbed (first irrigation, following cultivation or traffic,
etc.). Lower PAM rates can be used if good soil erosion control is achieved.
Excessive application of PAM can lower infiltration rate or suspend solids
in water, rather than promoting settling.
When using PAM, increase furrow inflow rates to prevent longer advance
time and excessive infiltration at the upper end of the field. PAM partially alleviates surface sealing in furrows. This maintains higher
infiltration rates throughout an irrigation than is usual with untreated
water. If irrigation practices are not adjusted, PAM use can worsen variability
of infiltration from upper to lower field ends. If inflow rates are increased
(doubled or tripled) during initial advance, and then reduced to the least
sustainable flow once runoff begins, erosion is still greatly reduced and
advance times shortened, thereby improving infiltration uniformity.
PAM applicators are available from numerous suppliers for application
of all PAM forms. Local PAM material suppliers can usually recommend vendors of several
styles of applicators suitable to their products. Good applicators seldom
cost more than a few hundred dollars. When considering applicators, look
for sturdiness and ability to calibrate application rate to match the water
flow. Liquid applicators and injectors should have back-flow protection,
and prevent condensation of water vapor in liquid delivery systems. WE
DO NOT RECOMMEND applying PAM as a pre-irrigation spray on furrow bottoms
using familiar agrichemical spray equipment. This application method has
not proven effective, and often risks gumming-up of the spray equipment,
since PAM can gel on contact with some concentrated chemical residues left
in sprayers, especially if dry wetable powders have been applied with the
When using PAM in Sprinklers. Benefits of using PAM with sprinkler irrigation are much less dramatic
than with furrow irrigation. Applying 2-4 lb PAM per acre can reduce erosion
and increase infiltration during the irrigation under some conditions.
However, beneficial effects last for only one or two irrigations. Many
questions are still unanswered about applying PAM through sprinkler systems.
It is a good practice to pump crop oil through the injection pump, hose
and valves before injecting PAM. Crop oil coats the inside of the equipment
which simplifies cleanup and removes any water that may have condensed
inside during storage. The injection pump, hose and valves should also
be flushed with crop oil immediately after PAM application is complete.
Crop oil removes the PAM without problems that are caused by adding water
to PAM. Do not try to clean injection equipment with water unless you want
to disassemble the equipment and flush each piece with copious amounts
of water. Crop oil greatly simplifies equipment clean-up.
ALWAYS have a check valve between the injection hose and the irrigation
line to prevent irrigation water from flowing back through the injection
line. If an injection pump or hose fails without a check valve, a soupy,
jelly mess will occur that is nearly impossible to clean up.
PAM has been shown to greatly improve water quality of irrigation runoff
from individualfields and district-wide return flows. Sediment, phosphorus, nitrogen, biological and chemical oxygen demand,
pesticide content, weed seed and microorganism content of irrigation return
flows have all been shown to be reduced by use of PAM for irrigation induced
erosion control. No negative environmental impacts from PAM, or from the
small amounts of AMD contained in registered PAMs, used at recommended
rates, have ever been demonstrated for surface waters or soil. PAM is and
will continue to be a powerful environmental and farming benefit if responsibly
used. For more complete and technically detailed information on PAM and
its use for irrigation-induced erosion control and for infiltration management, visit the PAM information website at the
PAM Research Page.